Sources of noise can be classified in different ways depending on the features or properties of the sources considered. Thus, noise sources can be classified due to:

I. Physical reasons for sound generation (in Polish: Engel Z., Pleban D., Noise of machines and devices - sources, evaluation, CIOP, 2001):

• mechanical sources (eg vibrations, impacts, friction),
• electric sources (eg magnetic, magnetostrictive),
• technological sources (eg cutting process, cracking process),
• aero and hydrodynamic sources, including flows (eg turbulence, gas outflow from the nozzle) and cavitation,
• other sources (eg combustion process, thermal phenomena, explosions).

II. The origin of sources (in Polish: Engel Z., Pleban D., Hałas machines and devices - sources, assessment, CIOP, 2001):

• means of communication and transport, including airplanes, road vehicles, special vehicles, rail vehicles, water vehicles, agricultural vehicles, trolleybuses, recreational vehicles,
• internal industrial sources (eg engines, generators, machine tools, presses, blowers, compressors, transformers, saws gears, pneumatic tools) and external (eg compressors, forges, chimneys, cooling towers, external conveyors, engine brakes, overhead cranes),
• construction, road, municipal and agricultural machinery (eg cranes, bulldozers, excavators, rollers, compressors, hammers and piles, cement mixers, drilling rigs, rammers, loaders, wood and forest machines),
• machines, devices and installations in buildings (eg transformers, cranes, hydrophores, water and sewage installations, ventilation and air-conditioning systems, office and computer equipment, signaling devices),
• municipal, environmental and military facilities (eg gas switching stations, bus depots, stations, airports, polygons, shooting ranges),
• natural sources (eg wind, waves).

III. Sound source affiliation to a specific group of machines or devices (Koradecka D. (ed.), Health and safety at work, CIOP-PIB, 2008):

• machines constituting a source of energy (eg internal combustion engines, compressors, transformers),
• pneumatic tools and motors (eg grinders, hammers, riveting tools, scrapers, rammers),
• plastic forming machines (eg presses, hammers, rolling mills),
• machines for grinding, crushing, sifting, cutting, cleaning (vibrating sieves, shock grids, ball mills, gritters),
• metalworking machine tools (lathes, grinders, milling machines, drills),
• woodworking machine tools (chainsaws, planers, millers, grinders, circular and band saws),
• textile machines (looms, spinning machines, twisters, rewinders, carding machines, warp knitters),
• flow devices (fans, valves, reducers, streamers, burners),
• internal transport devices (conveyors, feeders, overhead).

The source of noise understood as sounds harmful to the hearing organ are not only industrial machines and equipment. Exposure of employees to harmful sounds, the production of which is at the same time the essence of the work performed occurs in the profession of musician and music teacher. The level of sound reaching the music teacher depends mainly on the type of instrument on which the student plays, the repertoire practiced in class, as well as on the type of room in which the classes take place (size, acoustic adaptation used).

Table 1 shows the values of Equivalent A-weighted sound pressure level (L_Aeq,T), maximum A-weighted sound pressure level  (L_Amax) i peak C-weighted sound pressure level(L_Cpeak), to which music teachers conducting classes on various instruments may be exposed.

Table 1. Equivalent A-weighted sound pressure level, maximum A-weighted sound pressure level and peak C-weighted sound pressure level, occurring during classes in playing instruments and learning to sing